While every mapmaker strives to make the most visually appealing map they can imagine, you have to remember that the purpose of a map is to convey data clearly to your audience. In my career, I have made maps for planners, engineers, rangers, hydrologists, lawyers, field crews, surveyors, elected officials, and the public, just to name a few. If I was working on one project that involved all of those groups, each map of that project would be different than the other. Finding out who the audience of a map is? should be one of your first objectives.
With this figured out, you have a clearer goal of what data you will need and how to show it. Don't be afraid to ask questions; a lot of times you can be pulled into a project in which you have no background. It is more appropriate to ask a lot of questions in the beginning, rather than in the middle or towards the end of a project.
I typically ask the following questions when I get pulled into a project:
With these questions answered, I can usually feel comfortable enough to start a project. This will help me form a guide on how to formulate a work plan to solve this mapping problem.
Because mapping is becoming more accessible to people, there is a higher demand for it. People understand the power of showing data on a map, but may not understand the complexity of creating a great map. It is important to lay out realistic expectations when creating a map. It is really easy to put too much information into a map, which will only confuse the audience, and make the map look poor, as well. Not that it's impossible to have a lot of data in your map; it just takes a lot longer than most people expect and skills learned over many years of cartography experience.
A lot of people, myself included, can get excited about a project and want to immediately start working on it. Going out looking for any and all data or starting the design of the layout may be exciting, but this eagerness can cost you in the long run, as you will perform work that might not be used in the project. The beginning of a mapping project should move slowly at first, to mitigate unnecessary work.